Atropic rhinitis is prevalent in various countries of the world and causes severe economic losses in the swine-raising industry in terms of both inhibition of growth and reduction of feed efficiency. The causative agent for this disease has been shown to be B. bronchiseptica. At least 1.8 million cases occur in the U.S. alone each year and entire herds may become infected before clinical signs appear. Once apparent, the effect in terms of morbitity is essentially irreversible despite the use of antibiotics. Therefore, prophylaxis rather than cure is the only way to control this disease.